1. Field of the Invention
The embodiments described herein relate generally to X-ray diffraction imaging systems and, more particularly, to a method to calibrate and correct for inaccuracies in X-ray source focus point positions.
2. Description of Prior/Related Art
At least some known security detection systems are used at travel checkpoints to inspect carry-on and/or checked bags for contraband, such as concealed weapons, narcotics, and/or explosives. Further, at least some of these known security detection systems include X-ray imaging systems. In an X-ray imaging system, an X-ray source transmits X-ray radiation through a container, for example a suitcase, towards a detector. The detector outputs are processed to identify a set of objects and/or materials in the container. In addition, at least some known X-ray imaging systems used in security detection systems include X-ray diffraction imaging (XDI) systems. At least some known XDI systems use inverse fan-beam geometry (a large source and a small detector) and a multi-focus X-ray source (MFXS). Further, at least some known XDI systems provide an improved discrimination of materials, as compared to that provided by other known X-ray imaging systems, by measuring d-spacings between lattice planes of micro-crystals in materials to perform an X-ray diffraction analysis. X-ray diffraction may yield data from a molecular interference function that may be used to identify other materials, such as liquids, in a container.
In at least some known XDI systems having an MFXS, all focus point positions of the MFXS should lie along a straight line in the a scan plane to generate an optimal X-ray diffraction image. The focus point positions are, however, in practice affected by manufacturing inaccuracies and/or thermo-mechanical effects, such as expansion. As such, the focus point positions in known XDI systems do not lie along a straight line but, rather, are offset from the straight line by varying distances. Such offsets cause the focus point positions to be inaccurate. Inaccuracies of the focus point positions in an MFXS system may cause momentum blurring in a generated diffraction profile and/or a poor detection rate because of the angular blurring.
Accordingly, it is desirable to calibrate and/or correct for focus point position inaccuracies to generate sharper diffraction profiles, as compared to images that include blurring from focus point position inaccuracies.